The applanation technique has been used at least since 1957 when was developed the Goldman tonometer for ophtalmologyc use (see Amaral et al. Arquivos Brasileiros de Oftalmologia 69:41-45, 2006). In plants, Berstein & Lustig (see Vitis 20:15-21, 1981; Scientia Horticulturae 25:129-136, 1985) were pioneers in the use of this technique on grape berries and on others similar juicy fruits. Calbo & Calbo (see Revista Brasileira de Fisiologia Vegetal 1:41-45, 1989) has extended the principles of this measurement, which was applied to organs that could be treated as a membrane surrounded sphere, for other convex organs with regular and parenchymal dermal tissue. Two simple applanator models and one fast procedure for kneaded area evaluation were developed by Calbo & Nery (see Horticultura Brasileira 12:14-18, 1995), together with some contour conditions attended for cell turgidity dependent firmness measurements validation.
The reversible cell deformation occurrence during firmness measurements by applanation technique were subsequently evidenced (see Calbo et al. Annals of Botany 76:365-370, 1995; Pereira & Calbo Pesquisa Agropecuária Brasileira 35:2429-2436, 2000). Additionally, Calbo & Nery (see Brazilian Archives of Biology and Technology 44:41-48, 2001) have shown that for some cellular arrangement types may have simple mathematics relationship between firmness measured with applanation technique and the cell turgor pressure on tissues having thin cell wall, measured by intercellular gaseous volumes percent initially contained in the tissues.
Nowadays the firmness measure of fruits and vegetables by applanation has been used, mostly in Brazil, because it is a firmness measure dependent of physiology and of the hydric state of the plant which can be made repeatedly in a same organ. Then for genotypes selection, Andrade et al., (see Pesquisa Agropecuária Brasileira 40:555-561, 2005) have developed a criterion for determination of conservation half-life for tomato fruits enabling fruits selection with bigger storage capacity. This statistics technology can be extended to several other climacteric fruits. For guava and mango the applanation technique has been used for determination of firmness lost of these fruits caused by maturing. In vegetables as eggplant, beet (see Kluge et al. Scientia Agrícola 56:1045-1050, 1999) and carrot (see Calbo Bragantia 59:7-10, 2000; Caron et al. Horticultura Brasileira 21:597-600, 2003) the applanation technique has been used to determine firmness lost caused by transpiration during storage. For engineering purposes firmness measurements of fruits and vegetables by applanation technique together with the use of a simple mathematic model have turned possible determining the maximum height for product stacking and determining the package maximum height for the majority of fruits and vegetables marketed in Brazil (see Luengo et al. Horticultura Brasileira 21:704-707, 2003; Luengo, Doctorade Thesis, Escola Superior de Agricultura Luiz de Queiroz, Piracicaba, 77 p, 2006).
The applanation technique as described by Calbo & Nery (see Horticultura Brasileira 12:14-18, 1995) applies to firmness measurement of convex organs with regular and parenchymal dermal tissue. Then organs with irregularities, laminar organs and segmented organs require the development of specific procedures for their suitability measurement. For these applications, a porous tip applanation system for the application of applanation technique was tested for the comparison of water-lack stress effects during lettuce cultivation in pot (see Calbo III Congresso Brasileiro de Fisiologia Vegetal, Viçosa, 1991). Despite promising, the obtained results with that applanation system resulted in an expressive deformation of the leaf on the porous tip edge (2), reason why the use of that type of instrument was interrupted.
Systems in which compression applies can also be used for other purposes. Then, Shayo-Ngowi & Campbell (see Agronomy Journal 72:567-568, 1980) developed “hydraulic press” for water tension estimation on leaves and segmented tissues. For this type of segments measurement, typically with 25 mm2 area and up to 3 mm thickness, segments are compressed under the transparent glass plate until sap start exit from the compressed segment vascular bundles. According to Eldrege & Shock (see American Potato Journal 67:307-312, 1990) the method “hydraulic press” has presented a good correlation with the water tension measured with the pressure chamber on potatoes leaves. This author however draws attention to the lack of theoretical basis for the use of the “hydraulic press”, deficiency that is actually partially overcame by the developments showed in the works of Calbo et al. (see Annals of Botany 76:365-370, 1995) and Calbo & Nery (see Brazilian Archives of Biology and Technology 44:41-48, 2001).
The leaves' firmness measurement, on the other hand, has been considered not well resolved. An alternative for the firmness leaves hydration dependent measurement was described by Heathcote et al. (see Journal of Experimental Botany 30:811-816, 1979). On the test tip having a round cavity, the leaf surface deformation was induced by pressing a stick centralized on the leaf blade. Alternatively the leaf was pressed with a plate, acting in the middle of parallel bars, against which the leaf was supported. The distance between these bars must be as bigger as thicker and harder is the leaf. As described by Turner & Sobrado (see Journal of Experimental Botany 34:1562-1568, 1983), this type of method is sensitive to the leaf blade thickness and hence is difficult the comparison between different leaves, even being of one unique plant. Additionally the irregularities and veins distribution are important variation sources for the use of analog methods as recommended by Heathcote et al. (see Journal of Experimental Botany 30:811-816, 1979).
In this invention, it is described a novel applanator type for firmness measurement dependent of leaves cell turgor and of planar segments of organs which solve the majority of the limitations presented by the systems previously developed. This new applanation system makes use of a screen containing a porous element by which air flows, and due to its compression system it is useful for firmness measurement of leaves and planar segments of organs, as fruits and vegetables, since they are made of soft tissues where the firmness is modulated by the turgor pressure inside cells having fine structure cell walls.